The long-term objective of the proposed research is to gain a better understanding of gait abnormalities in Parkinson disease (PD). The experiments focus on 1) how decreased arm swing may be related to bradykinesia and/or rigidity, 2) exploring the mechanisms underlying turning difficulties and freezing and 3) adaptive capacity in the control of locomotor trajectory after stepping on a rotating treadmill in subjects with PD. Specific Aim 1 explores the relationships among arm swing, bradykinesia and rigidity. Specific Aim 2 examines the kinematic and electromyographic characteristics of turning and freezing. Specific Aim 3 looks at the effect of podokinetic stimulation (i.e. stepping on a rotating treadmill) and the applicability of using the rotating treadmill as a rehabilitative tool. Previous studies have noted that healthy individuals, following an adaptation phase of stepping on a rotating treadmill, inadvertently turn when asked to walk in place. We want to determine whether PD subjects demonstrate this adaptive response and furthermore whether treadmill training can enhance turning. The proposed research is very relevant to public health. PD is a neurodegenerative disease that affects more than 1 million people in America. As the US population ages the prevalence of PD will progressively increase and involve more of the general population. Addressing problems with walking in this patient population is crucial because these problems can pose a threat to functional independence. Moreover, turning difficulties may increase risks for falls, potentially leading to more complications. [unreadable] [unreadable] [unreadable]